Electronic article surveillance (“EAS”) systems are commonly used in retail stores and other settings to prevent the unauthorized removal of goods from a protected area. Typically, a detection system is configured at an exit from the protected area, which comprises one or more transmitters and antennas (“pedestals”) capable of generating an electromagnetic field across the exit, known as the “interrogation zone”. Articles to be protected are tagged with an EAS marker that, when active, generates an electromagnetic response signal when passed through this interrogation zone. An antenna and receiver in the same or another “pedestal” detects this response signal and generates an alarm.
Because of the nature of this process, other magnetic materials or metal, such as metal shopping carts, in proximity to the EAS marker or the transmitter may interfere with the optimal performance of the EAS system. Further, some unscrupulous individuals utilize EAS marker shielding, such as bags that are lined with metal foil, with the intention to shoplift merchandise without detection from any EAS system. The metal lining of these bags can shield tagged merchandise from the EAS detection system.
Conventional systems for detecting metals and magnetic materials are known, for example, U.S. Pat. No. 4,709,213, entitled “Metal Detector Having Digital Signal Processing,” U.S. Pat. No. 5,414,411, entitled “Pulse Induction Metal Detector,” and United States Patent Application Publication No. 2007/0046288, entitled “Hybrid-Technology Metal Detector”. Prior systems for using metal detection with EAS systems have also been suggested generally, for example, European Patent No. EP0736850, entitled “Method for preventing shoplifting and electronic theft detection system.” However, systems such as these merely provide a metal detection system adjacent to an EAS system, but do not provide any disclosure for the increased efficiency and cost reduction of actually combining these disparate elements into one system.
While EAS marker shielding detectors and metal detectors in general are reliable, they do have weaknesses. For example, merchandise, such as a case of soda cans, can mimic the response of a foil-lined bag due to surface area similarities and trigger false alarms. Thus, the presence of legitimately purchased items may affect the overall reliability of the EAS system. False alarms from metal detectors detract from the merchants' confidence and hurt sales of such systems.
Therefore, what is needed is a system and method for an EAS system to detect metals and more accurately determine whether a detected metal is an EAS marker shield, dependent upon the presence of a person in the interrogation zone and/or the direction the person is moving.